System and method for emulating a surface EKG using internal cardiac signals sensed by an implantable medical device

Abstract

A surface electrocardiogram (EKG) is emulated using signals detected by the internal leads of an implanted device. In one example, the emulation is performed using a technique that concatenates portions of signals sensed using different electrodes, such as by combining far-field ventricular signals sensed in the atria with far-field atrial signals sensed in the ventricles or by combining near-field signals sensed in the atria with near-field signals sensed in the ventricles. In another example, the emulation is performed using a technique that selectively amplifies or attenuates portions of a single signal sensed using a single pair of electrodes, such as by attenuating near-field portions of an atrial unipolar signal relative to far-field portions of the same signal or by attenuating atrial portions of a cross-chamber signal relative to ventricular portions to the same signal. The surface EKG emulation may be performed by the implanted device itself or by an external programmer based on cardiac signals transmitted thereto.

1. A method for emulating a surface electrocardiogram (EKG) of a patient in which an implantable cardiac stimulation device is implanted, the method comprising:
 sensing a single cardiac signal within the heart; 
 distinguishing portions of the single cardiac signal corresponding to atrial signals from those corresponding to ventricular signals; and 
 adjusting relative amplitudes of the portions of the single cardiac signal corresponding to atrial signals and the portions corresponding to ventricular signals so as to yield an emulated surface EKG using only the single cardiac signal with the adjusted relative amplitudes. 
 
   
   
     2. The method of  claim 1  wherein sensing a single cardiac signal is performed to sense an atrial unipolar signal using a lead implanted within the heart. 
   
   
     3. The method of  claim 2  wherein distinguishing portions of the single cardiac signals comprises:
 identifying near-field atrial signals within the atrial unipolar signal; and 
 identifying far-field ventricular signals within the atrial unipolar signal. 
 
   
   
     4. The method of  claim 3  wherein adjusting the relative amplitudes of the portions of the single cardiac signal comprises:
 determining a value representative of the peak magnitude of the near-field atrial signals; 
 determining a value representative of the peak magnitude of the far-field ventricular signals; and 
 adjusting the relative magnitudes of the near-field atrial signals and the far-field ventricular signals so as to achieve a predetermined ratio of peak atrial to peak ventricular magnitude. 
 
   
   
     5. The method of  claim 4  wherein the predetermined ratio of peak atrial to peak ventricular magnitude is in the range of 1:4 to 1:10. 
   
   
     6. The method of  claim 1  wherein adjusting the relative amplitudes of the portions of the single cardiac signal comprises:
 determining a value representative of the peak magnitude of the atrial signals; 
 determining a value representative of the peak magnitude of the ventricular signals; and 
 adjusting the relative magnitudes of the atrial signals and the ventricular signals so as to achieve a predetermined ratio of peak atrial to peak ventricular magnitude. 
 
   
   
     7. The method of  claim 6  wherein the predetermined ratio of peak atrial to peak ventricular magnitude is in the range of 1:4 to 1:10. 
   
   
     8. The method of  claim 1  wherein adjusting relative amplitudes of the portions of the single cardiac signal further comprises smoothing the adjusted signal. 
   
   
     9. The method of  claim 1  further comprising controlling device functions based, in part, on the emulated surface EKG. 
   
   
     10. The method of  claim 1  performed entirely by the implantable medical device. 
   
   
     11. The method of  claim 1  performed by the implantable medical device in combination with a device external to the patient and further comprising transmitting the cardiac signal to the external device and wherein the steps of distinguishing portions of the cardiac signals and adjusting relative amplitudes of the portions of the cardiac signal to yield an emulated surface EKG are performed by the external device. 
   
   
     12. A system for emulating a surface electrocardiogram (EKG) of a patient, the system comprising:
 input circuitry operative to input a single cardiac signal sensed by a device implanted within the patient; 
 a surface EKG emulation controller operative to distinguish portions of the single cardiac signal corresponding to atrial signals from those corresponding to ventricular signals and to adjust relative amplitudes of the portions of the cardiac signal corresponding to atrial signals and the portions corresponding to ventricular signals so as to yield an emulated surface EKG using only the single cardiac signal with the adjusted relative amplitudes. 
 
   
   
     13. A system for use in an implantable medical device for emulating a surface electrocardiogram (EKG) of a patient in which the device is implanted, the system comprising:
 means for sensing a single cardiac signal; 
 means for distinguishing portions of the single cardiac signal corresponding to near-field atrial signals from those corresponding to far-field ventricular signals; and 
 means for adjusting the relative amplitudes of the portions of the cardiac signal corresponding to near-field atrial signals and the portions corresponding to far-field ventricular signals so as to yield an emulated surface EKG using only the single cardiac signal with the adjusted relative amplitudes.